You CAN block Flash ads. And scripts, images, applets -- any URL. You just need to find out the URL first. Some sites have made this obviously difficult, since they need those ads for revenue.
You can read this thread:
http://forums.omnigroup.com/showthread.php?t=991 for a way to download a list of known ad servers and add it to OW's ad-blocker. The ingenious method is admittedly a little difficult, but it works with such a long list.
You can also visit
http://pgl.yoyo.org for lists of known ad servers.
I have blocked 99% of the Ads, including Flash, on the sites I visit with a combination of OW's ad blocker and custom CSS files.